Concentric pipe tuyeres, have been applied and are used widely throughout the metals industry. An early patent on such a tuyere was French Patent 1,450,718, which described two concentric pipes to produce a core jet of oxygen surrounded by an annular jet of cooling gas. Since then, a large number of improvements have been made using either two concentric pipes as in French patent or two or more than two concentric pipes as shown in the following United States Patent
______________________________________ 2,855,293 3,893,658 4,272,286 3,706,549 3,897,048 4,336,064 3,832,161 4,022,447 4,450,005 3,891,492 4,138,098 4,754,951 4,249,719 4,887,800 ______________________________________
In order to operate satisfactorily any tuyere for injecting fuel gas and oxygen into a molten metal bath, the tuyere must be operated within very narrow limits. If the temperature is allowed to increase too much the tuyere pipes melt or burn away and the tuyere fails in a short time. If the temperature is too low, a solid accretion forms at the tip of the tuyere and the tuyere becomes blocked, the flow of gas out of the tuyere ceases and the gas is forced into the refractory surrounding the tuyere, with destruction of the refractory and failure of the tuyere.
In order to operate satisfactorily for extended periods of time, a tuyere for injecting fuel gas and oxygen into molten metals must remain cool, open, and must be protected by a thermal accretion of the correct size. Additionally, it must be constructed of materials that are compatible with the reactants at the operating temperatures, pressures, and velocities.